The notion of sharing the risk of failure is an important concept for route computing issues. The concept of shared risk groups (SRG) was introduced in order to identify network resources which may be collectively and jointly affected by a particular event, such as the failure of a piece of equipment functionally related to all resources belonging to the group. For example, within an optical network, a shared risk link group (SRLG) may be defined to designate all optical fibers which are located within a single physical conduit, and which therefore share the risk of interruption in the event that this conduit is damaged. Shared risk groups may also be defined for other types of network resources (nodes, links) and other types of shared risks (location within the same geographic area, the same building, reliance upon the same source of electrical power, etc.)
In practice, belonging to a shared risk group is indicated by associating a shared risk group identifier (SRG ID or SRLG ID) with this resource. A resource, such as a node or link, may belong to multiple shared risk groups at once. Shared risk information, i.e. the associations between a network's physical resources and the shared risk groups defined within this network, is relatively static information which may be collected in Interior Gateway Protocol messages, and stored within a traffic engineering database so that they may be used by a route-computing device, particularly in order to compute disjoint routes. Conventionally, a connection path is considered to “cross a shared risk group” whenever its connection path uses at least one resource associated with that shared risk group. Other details on using SRLGs may, for example, be found in “Shared Risk Link Groups Inference and Processing”, draft-papadimitriou-ccamp-srlg-processing-02, IETF, June 2003.
In order to allow them to operate and be administered, large modern networks, such as the Internet, are structured into domains, between which exchanges of information are subjected to certain restrictions. Examples of domains notably include routing domains, the areas and sub-areas of IGP routing protocols, and the autonomous systems (AS) of EGP routing protocols. These restrictions have both functional grounds, such as preserving the scalability of the network and preventing it from becoming overloaded, and administrative grounds, such as keeping certain information related to an operator's network confidential from other operators. In particular, shared risk information within an operator's network is sensitive data that may reveal vulnerabilities, and which must therefore be suitably protected.
With the development of IP (Internet Protocol) control plans based on the MPLS and GMPLS protocol stacks, it is possible to automate route computations and resource reservations in order to establish connections (LSP, for label-switched paths) having controlled traffic engineering characteristics (in terms of bandwidth, protection, etc.) across multi-domain networks. However, because of the restrictions imposed between domains, computing routes between domains remains an imperfectly solved problem, particularly when complex restrictions must be met.
One purpose of the invention is to facilitate the determination of disjoint routes in a multi-domain network. Another purpose of the invention is to enable the detection of a risk shared between connections of a client layer, said connections being embedded within connections of a server layer.